LITTLE ROCK (AP) — Abortion opponents urged Democratic U.S. Sen. Mark Pryor on Friday to support banning the procedure 20 weeks into a woman's pregnancy, an effort by conservatives to move social issues to the forefront of the nationally watched Arkansas race.

A coalition of groups rallied at the Arkansas state Capitol in favor of the measure, which prohibits abortions based on the disputed notion that a fetus can feel pain at 20 weeks. Republican rival and U.S. Rep. Tom Cotton voted for the ban last year in Congress, while Pryor has said he has constitutional concerns about the legislation.

Josh Duggar, the executive director of Family Research Council Action, warned Pryor he would "feel the pain" from voters if he didn't back the ban.

"If he's not willing to stand up and take a bold stand and do what's right for Arkansans, they're going to have their voice in November," Duggar said.

The U.S. House passed the ban last year, and an identical bill has been introduced in the Senate. The American College of Obstetricians and Gynecologists says it knows of no legitimate evidence that shows a fetus can experience pain.

The Arkansas Legislature approved a similar ban last year, overriding a veto by Democratic Gov. Mike Beebe that cited constitutional concerns. Courts have blocked similar prohibitions in Arizona, Georgia and Idaho.

Pryor has said he has similar concerns about the measure and couldn't support it.

"There have been a number of decisions that would indicate that's not constitutional," Pryor said Thursday. "I really think unless we can make it constitutional, I don't know what good it does to have that. I don't support it at this time, but I'll continue to look at it."

Former U.S. Rep. Marilyn Musgrave, vice president of government affairs for the anti-abortion Susan B. Anthony List, said Democratic Senate leaders were "protecting senators like your own Mark Pryor."

Pryor's campaign on Friday took aim at Cotton, who has co-sponsored legislation stating life begins at the moment of fertilization. Pryor's campaign said he's personally opposed to abortion.

"But when a doctor says that continuing a pregnancy threatens a mother's life or a girl becomes pregnant as a result of a rape or incest, then her family, her doctor and pastor should provide guidance," Pryor spokeswoman Mary Robbins said. "Congressman Cotton would have the government intervene. Cotton would make all abortions illegal with no exceptions for rape, incest or the life of the mother."

Cotton spokesman David Ray accused Pryor of being out of touch on the issue.

"Tom Cotton is proud to support legislation that prohibits gruesome abortions after unborn children can feel pain, and provides exceptions for extreme and tragic circumstances," Ray said. "Tom's record stands in stark contrast to Senator Pryor's support for late-term abortion and taxpayer funding for abortions, which is out-of-touch with Arkansas voters."

Pryor's campaign has called similar criticism in the past false, pointing to votes he's cast against federal funding for abortions and for a late-term abortion ban in 2003.

The rally, which was the final stop on a tour that also targeted incumbent Democratic senators in Colorado and North Carolina, was aimed at putting the focus on abortion in a race that has centered more on issues such as Social Security, the federal health care law and the economy.

Women Speak Out, SBA's political action committee, is spending $1 million to target Pryor and has three field offices around the state, the group said.